This proposal outlines a plan for the Merritt Peralta Institute Cancer Education and prevention Center participation as a clinical site in National Cancer Institute Phase III, multi-institutional, five-year cooperative trial of a low fat diet in women at increased risk for breast cancer. The Cancer Education and Prevention Center (CEPC) is a direct outgrowth of Merritt Hospital's participation in the ACS/NCI Breast Cancer Detection Demonstration Program in which 10,000 women were screened annually for breast cancer at Merritt Hospital between 1974-79. The CEPC has continued to offer breast screening services as well as comprehensive cancer screening and education to a large percentage of the women in the breast screening project, insuring access to the required size study population for this new NCI project. Furthermore, this proposal describes the CEPC's unique advantage in this undertaking because it has already made operational many of the methods called for in this project. The proposal is directly responsive to the NCI RFA 84-CA-01 and demonstrates the CEPC's ability to identify, enroll, and follow participants using a protocol developed jointly by the investigators and NCI staff. Three stages to the trial are addressed: protocol writing, feasibility testing (1st year), and full implementation to complete a five year study period. CEPC will enroll more than 200 women with an annual risk of breast cancer of at least 1% (i.e., women with a 1st degree relative with breast cancer and having additional risk factors of age of 1st pregnancy past 30, or two or more breast biopsies, or breast cancer in an additional 1st degree relative). This cohort of women will be randomized into a control and diet group of at least 100 women each. The diet group will have frequent group and individual nutritional counseling to attain the goal of reducing fat intake to 20% of calories. Both the control and study groups will be monitored extensively for nutritional compliance and safety, and screened for breast cancers by physical examination and annual mammograms. Data acquired will be analyzed and submitted as part of this timely collaborative, multi-institutional effort.